Attachments.me is a free service that can upload Gmail attachments directly to Dropbox (as well as Box, Google Drive, and SkyDrive). Just install its browser plug-in (available for Chrome and Firefox), then link it with one or more of the aforementioned cloud services. With that done, Attachments.me indexes all your attachments, then catalogs them for easy viewing and searching.

Microsoft Word, Excel, and PowerPoint on your iPad, with documents automatically syncing to and from Dropbox? It sounds almost too good to be true, yet that's exactly what you get from CloudOn. (In fact, the service recently announced plans to build more features on top of Office.) The really amazing part: CloudOn is free.

Think of Cue as an app aggregator: It presents your contacts, calendar, email, Facebook posts, Dropbox documents, and more under one convenient roof. The idea is to make all your most important events and stuff easily accessible, without the need to go hopping back and forth between various apps. And it does all this free of charge.

There are lots of apps that can turn your phone or tablet into a scanner, and plenty of those will sync those scans to Dropbox. JotNot Scanner Pro is on of them; for a mere $1.99, it quickly and easily scans, adjusts, and saves paper documents. It can even fax them for you.

A little bit Evernote, a little bit WorkFlowy, Paperless is simpler than the former and more versatile than the latter. It's a list-making app, suitable for everything from your daily to-do list to a rundown of presentation points. And it leverages your Dropbox account to back up your lists and sync them between your devices. Price: $2.99.

Have you found any other indispensable apps that sync with Dropbox? If so, tell me about them in the comments.

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For more than 20 years, Rick Broida has written about all manner of technology, from Amigas to business servers to PalmPilots. His credits include dozens of books, blogs, and magazines. He sleeps with an iPad under his pillow.